The present invention relates to a linear motor, and more particularly to a linear motor suitable for generating a greater or smaller thrust in a specific section or sections than the thrust generated during usual linear movement.
The linear motor derives from horizontal development of the configuration of a rotary motor, and is available in a variety including the following versions: for example, a linear D.C. motor (unipolar or multipolar), a linear synchronous motor, a linear induction motor and a linear pulse motor. To take up the linear pulse motor as an example, such a prior art linear motor is disclosed in JP-A-63-310361 specification.
Some machines to which the linear motor is applied require a considerably large thrust and braking force, while others do not. Some machines may require considerably large thrust and braking force only in a specific section or sections. Conceivably, such a machine which requires a considerably large thrust and braking force in a specific or sections may use over the whole operation range a linear motor of a structure capable of generating the required thrust and braking force. Where the linear motor itself is incapable of generating the required thrust and braking force, it is conceivable to use in each of such specific sections another special power source to generate the required thrust and braking force.
For instance, as described in JP-A-11-243676 specification , there is a method of using in a specific section or sections a mechanism for generating a greater thrust and braking force than the usual thrust and braking force by providing a mover runner with a slope tapering in its moving direction and the armature core of armature means to have an equal distance from this slope and branching part of a suction force arising between the mover runner and the armature core.
However, the above-cited example of the prior art requires structuring of a tapered slope in a specific part, i.e. altering the structure only in a specific part, resulting in the possible problem of a higher manufacturing cost.
An object of the present invention is to provide a linear motor capable of generating a greater thrust and braking force in a specific section or sections than the thrust and braking force during usual linear movement.
A characteristic of the present invention is that it is a linear motor having an armature and a needle with magnetism, in which the armature has at least a magnetic pole of a first polarity having a first opposed part and another magnetic pole of a second polarity having a second opposed part; the needle is held by the first opposed part, the needle is further held by the second opposed part; and a magnetic area in the needle is varied only in a prescribed section.
Or there is provided a linear motor having an armature and a needle with magnetism, in which the armature has at least a magnetic pole of a first polarity having a first opposed part and another magnetic pole of a second polarity having a second opposed part; the needle is held by the first opposed part and is further held by the second opposed part; and preferably a magnetic substance is used which permits the magnetism of the needle to vary according to a prescribed section or sections.